Heat Treatment of Solids

By injection of refractory powders into RF discharges, it is possible to heat treat the particles. Decomposition, vaporization, melting, or surface modification of particles can be achieved in varying degrees depending on the physical properties of the material, particle residence time, particle surface area, and the enthalpy available in the plasma. 

The first reported heat treatment of a solid in an RF plasma was carried out by Reed (43). He injected powders at high velocity through an atmospheric pressure argon plasma and deposited molten powder on a crystal boule in the plasma tail flame. A sapphire polycrystal, some 

An extension of the use of RF plasma for particle heating is the spheroidization of solids. By careful control of plasma enthalpy, particle size, feed rate, and feed position, it is possible to melt each particle as it passes through the plasma. The liquid droplet forms a sphere due to surface tension and, on cooling, retains its spherical shape. Spheroidized particles are commercially useful because they will flow easily. 

Waldie 56, 57), in an attempt to prepare ultrafine powders from coarser materials, obtained spheroids of oxide powders in low-power RF torches. When silica powder (50-72 p.m) was injected into a 2.5-kW, 34-MHz argon plasma at 15 gm/hr, a 15% conversion to ultrafine particles (0.015-0.15 / m) and coarse spheroids were obtained. Ultrafine powders of barium oxide (50% 0.1 ju.m) and alumina spheroids were also prepared by this technique. When alumina was injected cocur-rently into a 3.5-kW, 10-MHz argon plasma 57), 48% spheroidization of a 180-250 /xm powder was obtained at a feed rate of 36 gm/hr. Waldie obtained better results by use of countercurrent particle flow similar to the technique used by Haiti 26). Up to 26% spheroidization of a 300-500 /xm powder was measured for an alumina feed rate of up to 140 gm/hr. It is evident from this work that countercurrent spheroidization can achieve not only higher yields of spheroids but also spheroidization of a larger size range of solid. 

Warren and Shimizu 59) injected single oxides and oxide concentrates into a 2-MHz, 7-kW argon plasma. Alumina, silica, and niobium 

---

Reductive nitrosylation, transition metal nitrosyl complexes, 34 296-297 ReFejSj cluster, 38 41-43 self-assembly system, 38 41-42 Refining, of actinide metals, see Actinide, metals, purification Refractory compounds heat treatment of solids, 17 105-110 crystal growth, 17 105, 106 decomposition, 17 107,-110 spheroidization, 17 106, 107 preparation of, using radio-frequency plasma, 17 99-102... 

Figure 5.9 Heat treatment of solid iron containing carbon.

B. Hydrogen Cyanide and Cyanogen VTI. Heat Treatment of Solids... 

During the heat treatment of solids, elements in solution tend to segregate and ac-... 

In contrast to X-ray diffractometry, DSA makes it possible to investigate poorly crystalline or amorphous solids. In contrast to adsorption measurements for surface area determination, DSA permits a continuous investigation of the surface, even at elevated temperatures during heat treatment of solid samples or their hydration, under wet conditions, without the necessity of interrupting the heat treatment or the hydration and cooling the sample to liquid nitrogen temperatures. For this reason, the DSA may reflect the nature of the surface at elevated temperatures more accurately than adsorption measurements. 

Heat Treatment Heat treatment can be divided into two types, treatment of fluidizable solids and treatment of large, usually metallic objects in a fluid bed. The former is generally accomplished in nmlti-compartment units to conserve heat (Fig. 17-27). The heat treatment of large metallic objects is accomplished in long, narrow heated beds. 

Khare N, Razzini G, Peraldo Bicelli L (1990) Electrodeposition and heat treatment of CuInSei films. Thin Solid Films 186 113-128... 

CNTs can also be produced by diffusion flame synthesis, electrolysis, use of solar energy, heat treatment of a polymer, and low temperature solid pyrolysis. In flame synthesis, combustion of a portion of the hydrocarbon gas provides the elevated temperature required, with the remaining fuel conveniently serving as the required hydrocarbon reagent. Hence, the flame constitutes an efficient source of both energy and hydrocarbon raw material. Combustion synthesis has been shown to be scalable for a high volume commercial production. 

The total emission In the commercial heat treatment of 5 to 8 hours at 170 to 160°C varied from 0.4 to 1.2% for CO2 and 0.05 to 0.2% for CO and 0.04 to 0.1% for total acids based on dry board. Some of this emission might emanate from pyrolysis of higher molecular weight material condensed and deposited on the walls of the heat treatment chamber. The heat of formation of this CO2 and CO Is about half the total heat release measured. Part of the oxidation products might remain in the solid phase within the board material, e.g. as bound carbonyl and carboxylic groups, partly followed by heat consuming dehydration reaction. 

The absolute value of the entropy of a compound is obtained directly by integration of the heat capacity from 0 K. The main contributions to the heat capacity and thus to the entropy are discussed in this chapter. Microscopic descriptions of the heat capacity of solids, liquids and gases range from simple classical approaches to complex lattice dynamical treatments. The relatively simple models that have been around for some time will be described in some detail. These models are, because of their simplicity, very useful for estimating heat capacities and for relating the heat capacity to the physical and chemical... 

Heat Treatment Heat treatment can be divided into two types, treatment of fluidizable solids and treatment of large, usually metallic objects in a fluid bed. The former is generally accomplished in multicompartment units to conserve heat (Fig. 17-28). The heat treatment of large metallic objects is accomplishecTin long, narrow heated beds. The objects are conveyed through the beds by an overhead conveyor system. Fluid beds are used because of the high heat-transfer rate and uniform temperature. See Reindl, Fluid Bed Technology, American Society for Metals, Cincinnati, Sept. 23, 1981 Fennell, Ind. Heat., 48, 9, 36 (September 1981). 

To reduce further the pore size and/or to introduce specific interactions between the solid surface and the liquid or gaseous medium in the pores, sol-gel layers need to be modified. In principle this is done by precipitation or by adsorption of components from a gaseous or liquid medium followed by heat treatment of the formed products inside the pores or the pore entrance. This will be further discussed in Section 2.7. 

A. Hirata, M. Igarashi, T. Kaito, Study on solid lubricant properties of carbon onions produced by heat treatment of diamond clusters and particles. Tribology Int., 37(11-12) (2004) 899-905. 

Experiments were also carried out at 80 and lOO C. According to our observations at these high temperatures, solid- phase chemical transformations may take place between certain flavor constituents and cyclodextrin hydroxyls/monoterpene alcohols and phenolic compounds appear as a result of a solid-phase transacetylation of terpeneaoetates and phenyl-acetates with the simultaneous formation of cyclodextrin-acetates/. Long term heat treatments of cyclpdextrin-flavor complexes should not be run above 6o°C in order to avoid such phenomena. 

Thermal Inhibition, Heat treatment of milk is the most important practical means of inactivating its lipases. The temperature-time relationship necessary for partial or complete inactivation has been extensively studied, but a number of discrepancies have been apparent. These are probably due to several factors, including the sensitivity of the assay procedure, the length of the incubation period following heating, the presence and concentration of fat and solids-not-fat in the milk at the time of heating, and the type and condition of the substrate. In view of these variables, references to a number of early studies on heat inactivation have been omitted. 

The basic oxygen process produces steels that contain about 1% carbon but only very small amounts of phosphorus and sulfur. Usually, the composition of the liquid steel is monitored by chemical analysis, and the amounts of oxygen and impure iron used are adjusted to achieve the desired concentrations of carbon and other impurities. The hardness, strength, and malleability of the steel depend on its chemical composition, on the rate at which the liquid steel is cooled, and on subsequent heat treatment of the solid. The mechanical and chemical properties of a steel can also be altered by adding other metals. Stainless steel, for example, is a... 

Calcium carbonate, mother-of-pearl, magnesite, dolomite and other inorganic materials which nature uses to provide an organism with solidity, have been categorized under the name bioceramic materials. Later some synthetic materials were added to this group. This means that the definition of a ceramic material, as given at the beginning of this book, must somewhat be adjusted as the heat treatment of a ceramic material obviously does not apply in the animal world. 

---